1. Field of the Invention
The present invention relates to a traffic signal control method for setting a time on a green light (hereinafter, referred to as the green light time) to a value between the lower limit time and the upper limit time in real time depending on a traffic volume sensed by a vehicle sensor or the like.
2. Description of the Related Art
Conventionally, the green light time of a traffic signal is controlled in the manner as follows.
Vehicle sensors (a device capable of detecting a passing vehicle, such as an inductive loop sensor, an ultrasonic sensor and a camera; ditto for the description below) are set up for respective access roads to an intersection, and in a case where a traffic volume (the number of passing vehicles per unit time) is less than a predetermined value when the lower limit time has passed since the traffic signal turned to a green light, the green light is turned off and the control flow proceeds to the following step (yellow light). The green light time is extended in a case where the traffic volume is equal to or greater than the predetermined value. It should be noted, however, that the green light is turned off forcedly regardless of the traffic volume when the upper limit time has passed, and the control flow proceeds to the following step (yellow light).
Because the upper limit time is fixed in the conventional method, the green light time cannot be extended over the upper limit time even in a case where a traffic volume in one direction is far heavier than in any other direction, for example. However, traffic jam (an extraordinary large number of vehicles are waiting on a red light) will not be solved unless the green light time is extended as needed over the upper limit time.
Accordingly, there has been an increasing need for a traffic signal control method capable of setting the upper limit time of a green light flexibly in real time depending on a traffic volume.